Expression of the SM‐20 Gene Promotes Death in Nerve Growth Factor‐Dependent Sympathetic Neurons

Abstract

Sympathetic neurons undergo apoptosis when deprived of nerve growth factor (NGF). Inhibitors of RNA or protein synthesis block this death, suggesting that gene expression is important for apoptosis in this system. We have identified SM-20 as a new gene that increases in expression in sympathetic neurons after NGF withdrawal. Expression of SM-20 also increases during neuronal death caused by cytosine arabinoside or the phosphatidylinositol 3-kinase inhibitor LY294002. In addition, SM-20 protein synthesis is elevated in NGF-deprived neurons compared with neurons maintained with NGF. Importantly, expression of SM-20 in sympathetic neurons causes cell death in the presence of NGF. These results suggest that SM-20 may function to regulate cell death in neurons. Key Words: Nerve growth factor-Apoptosis-Sympathetic neuron-Gene expression-Cell death. J. Neurochem. 73, 429 -432 (1999).Inhibitors of RNA or protein synthesis block neuronal death after neurotrophic factor deprivation (Martin et al., 1988;Scott and Davies, 1990;Milligan et al., 1994), suggesting that gene expression may be important for regulating this kind of cell death. Consistent with this hypothesis, a small number of genes has been identified that increase in expression in sympathetic neurons after removal of nerve growth factor (NGF) Freeman et al., 1994;Ham et al., 1995). These genes, which include c-jun, JunB, cyclin D1, c-myb, c-fos, FosB, NGFI-A, and Mkp-1, are maximally expressed 10 -20 h after NGF withdrawal, generally preceding the onset of cell death in this system. Several reports suggest the involvement of c-jun and cyclin D1 in neuronal death. Blocking c-Jun function with c-Junneutralizing antibodies or dominant-negative forms of c-Jun protects sympathetic neurons and PC12 cells from death caused by NGF withdrawal and cerebellar granule neurons from withdrawal of insulin-like growth factor-1 Ham et al., 1995;Xia et al., 1995;Watson et al., 1998). Moreover, overexpression of c-Jun is sufficient to induce death in the presence of neurotrophic factors (Ham et al., 1995;Watson et al., 1998). Cyclin D1 protein content and cyclin-dependent protein kinase activity increase during death of serum-deprived N1E-115 neuroblastoma cells, and expression of a cyclindependent protein kinase inhibitor blocks the death (Kranenburg et al., 1996). Cyclin D1-associated kinase activity also increases in cortical neurons undergoing death induced by DNA damage (Park et al., 1998), and cyclin-dependent protein kinase inhibitors can reduce death in neurons deprived of NGF (Park et al., 1997).We now describe an additional gene, called SM-20, that is selectively expressed in sympathetic neurons after NGF withdrawal. SM-20 was originally identified as a growth factorresponsive gene in vascular smooth muscle cells (Wax et al., 1994). SM-20 expression has also been detected after activation of a temperature-sensitive p53 protein in fibroblasts; in these cells p53 activation results in both growth arrest and apoptosis (Madden et al., 1996). Although the biochemic...

HIF in Kidney Disease and Development

“…128 Growth factor signaling by nerve growth factor (NGF) in sympathetic neurons has been shown to inhibit PHD expression. 129,130 Under hypoxia, PHD1, and PHD3 are targeted for proteasomal destruction by the E3 ligases Siah1/2. HIF-1␣ is expressed in most renal epithelial cells, whereas HIF-2␣ is mainly found in endothelial cells and renal interstitial fibroblast-like cells in response to hypoxia, ROS, NO, NGF, and Toll-like receptor 4 (TLR4) activation or NF-B signaling in myeloid cells (not shown).…”

Novel estrogen and tamoxifen induced genes identified by SAGE (Serial Analysis of Gene Expression)

“…However, similar to SM-20, EIT-6 is also induced by various growth agonists (EGF, isoproterenol, and PMA) in ZR75-1 cells (data not shown). The rat SM-20 cDNA was also identi®ed as a gene induced by wild-type p53 and as a gene induced in sympathetic neurons during NGF (Nerve Growth Factor) withdrawal initiated apoptosis (Lipscomb et al, 1999;Madden et al, 1996). Subsequent experiments in muscle cells determined that SM-20 may play a role in the regulation of myoblast proliferation and di erentiation (Moschella et al, 1999).…”

Falkor, a novel cell growth regulator isolated by a functional genetic screen

“…On the one hand, SM-20 was identified as a growth factor responsive gene in rat smooth muscle cells (Wax et al, 1994). On the other hand, it was also reported to be a p53 target gene in rat fibroblasts (Madden et al, 1996) and a mitochondrial apoptosis related gene in sympathetic neurons (Lipscomb et al, 1999(Lipscomb et al, , 2001. These seemingly contradicting reports may suggest that like other cell growth regulators, SM-20 has a distinct regulatory role in different cell types and under different conditions.…”

“…Interestingly, the Cterminal domain of Falkor that was isolated from the GSE library and from the mouse embryo cDNA library shares about 70% identity with a known rat and human protein, SM-20 (Dupuy et al, 2000;Wax et al, 1994). SM-20 was shown by several groups to have a role in cell growth regulation (Lipscomb et al, 1999;Madden et al, 1996;Wax et al, 1996). The C-terminal domains of both Falkor and SM-20 are evolutionarily conserved and have strong homology with a known C. elegans protein, EGL-9.…”